Effect of the matrix structure on vermicular graphite cast iron properties

Abstract

Vermicular graphite cast iron (VGCI) prepared via the sandwich process was treated by annealing, and the microstructure and the mechanical and damping properties before and after the annealing treatment were studied. The graphite size, distribution and morphology did not change significantly after annealing. However, the matrix transformed from ferrite + pearlite to ferrite after annealing, the dislocation density decreased significantly, and the interfacial stacking faults between the matrix and graphite disappeared. The annealing treatment reduced the tensile strength by >12%, but increased the strain-to-fracture value to two times that of the as-cast sample. The damping properties varied with temperature with obvious S-K peaks and Ge peaks. The maximum internal friction changed from 0.023 (as-cast) to 0.011 (post-anneal).

Production of Ductile Iron Using Inside-Mold Treatment Technique

“…In the cells in which a nickel-magnesium alloy was used, the microscopic structure as in Figure (7) was observed with the appearance of a spherical-like structure (Vermicular), where we notice the presence of nuclei scattered with a small number in the microscopic structure of the metal in addition to the graphite flakes we find distinguished by a large thickness in relation to the usual composition in Gray cast iron [9]. This composition shows that the reaction of the nickel-magnesium alloy was not carried out effectively to obtain the spherical structure, and that the amount of the added alloy, which is 0.5%, was not sufficient to produce the appropriate reaction to convert all the flakes.…”

Archives of Foundry Engineering

“…For many years, after the invention of spheroidal graphite cast the iron, in the 1950s and even 1960s, vermicular cast iron was regarded as an "unsuccessful" ductile iron. However, for some decades, the use of cast iron with vermicular graphite has been increasing [2][3][4][5][6]. Although the production of vermicular cast iron castings is considered very difficult, due to the requirement to keep the amount of spheroidizer in the alloy within strictly defined narrow limits [7], this type of cast iron is used to make, among other things: − castings of combustion engine blocks with a high degree of compression and a high combustion temperature of the mixture, engine heads, ingot moulds, piston rings, brake discs, exhaust manifolds [1]; − gears, parts of machine tools subjected to vibrations during operation, bodies of turbochargers [8]; − moulds for the glass industry [9].…”